Exceptional bryozoan assemblage of a microbial-dominated reef from the early Wenlock of Gotland, Sweden

Eleven bryozoan species were described from Nors Stenbrott (Gotland, Sweden), represented by six trepostomes, four cystoporates and one fenestrate. Three genera with three species are new: two cystoporates Acantholunaria expansa gen. n. sp. n. and Curviporamonostylata gen. n. sp. n., and a trepostome Stellatotrypa hirsuta gen. n. sp. n. Two trepostome species are new: Leptotrypa perforata sp. n. and Leptotrypa enodis sp. n. The described bryozoan fauna is dominated by thin encrusting taxa which are involved in intensive interactions with calcimicrobes in bryozoan-microbial crusts in the reef. The bryozoan-microbial crusts (bryoliths) show certain sequences by microbes, encrusting bryozoans and tabulate corals. Multiple self-overgrowth of bryozoans occurs frequently and is interpreted as a defensive tactic against microbial fouling. Bryozoans avoid vicinity to tabulate corals, apparently due to strong competition for substrate. The bryozoan fauna from Nors Stenbrott is highly endemic, only two species are known elsewhere (North America and Great Britain).